def isPrime(a):    if a == 1: return False    test = True    k = a - 1    while k > 1:        if not a % k:            test = False            break        k -= 1    return testn = input()r = []for i in range(len(n)):    for k in range(i + 1, len(n) + 1):        a = int(n[i:k])        if isPrime(a):            r += [a]print(max(r) if r else 0)